Contour Patterns & Cross Sections
Contour lines are one of the most powerful tools on a map. They allow you to visualise the three-dimensional shape of the land on a two-dimensional surface. At GCSE you need to be able to interpret contour patterns to identify landforms and draw accurate cross sections. This lesson covers both skills in detail.
What Are Contour Lines?
A contour line joins all the points that are at the same height above sea level. On OS maps:
- Contour lines are drawn in brown (or orange)
- The contour interval is usually 10 metres (i.e. each line represents a 10 m height difference)
- Every fifth contour line is drawn thicker and labelled with its height — these are called index contours (e.g. 50, 100, 150, 200)
- The numbers on contour lines always read so that uphill is at the top of the number
Exam Tip: If you cannot see a height label on a contour line, count up or down from the nearest index contour in steps of 10 m.
Reading Contour Patterns
The spacing of contour lines tells you about the steepness of the land:
| Contour Spacing | What It Means |
|---|
| Very close together | Very steep slope |
| Close together | Steep slope |
| Evenly spaced | Constant gradient |
| Far apart | Gentle slope |
| Very far apart / absent | Flat land or plateau |
Recognising Landforms from Contour Patterns
Hills and Mountains
- Concentric (roughly circular) contour lines with increasing values towards the centre
- The highest point is shown by a spot height or triangulation pillar
Valleys
- Contour lines form a V-shape or U-shape that points towards the higher ground
- In a V-shaped valley (formed by a river), the V points upstream (uphill)
- In a U-shaped valley (formed by a glacier), the contour lines are more widely-spaced at the valley floor with steep sides
Spurs
- A spur is a ridge of land jutting out from higher ground into lower ground
- Contour lines form a V-shape pointing downhill (towards the lower ground)
- Spurs are often found between two river valleys
Ridges
- A ridge is an elongated area of high ground
- Contour lines run roughly parallel along the length of the ridge
- The ridge line connects the highest points
Saddle (Col)
- A col or saddle is a low point between two areas of higher ground
- On a map it looks like a figure-of-eight pattern in the contour lines
- Paths and roads often cross through cols because they offer the lowest route between valleys
Escarpments
- An escarpment (or cuesta) has one steep slope (scarp slope) and one gentle slope (dip slope)
- On a map, one side shows closely-spaced contours (steep) and the other side shows widely-spaced contours (gentle)
Plateaux
- A plateau is an area of relatively flat, high ground
- On a map, the edges have closely-spaced contour lines (steep ascent) but the top has widely-spaced or absent contour lines
| Landform | Contour Pattern |
|---|
| Hill | Concentric circles, values increase towards centre |
| V-shaped valley | V-shape pointing upstream/uphill |
| U-shaped valley | Wide, flat floor; steep, parallel-contoured sides |
| Spur | V-shape pointing downhill/downstream |
| Ridge | Parallel contour lines along an elongated high area |
| Col / Saddle | Figure-of-eight between two peaks |
| Escarpment | Closely-spaced on one side, widely-spaced on the other |
| Plateau | Steep edges, flat (widely-spaced contours) on top |
Exam Tip: The difference between a valley and a spur confuses many students. Remember: in a valley the V points uphill (towards higher ground). For a spur the V points downhill (towards lower ground).
Gradient
Gradient measures how steep a slope is. It can be expressed as:
A Ratio
Gradient = vertical rise ÷ horizontal distance
Example: A slope rises 100 m over a horizontal distance of 500 m.
Gradient = 100 / 500 = 1/5 = 1 in 5 (or 1:5)
As a Percentage
Percentage gradient = (vertical rise / horizontal distance) × 100
Using the same example: (100 / 500) × 100 = 20%
How to Calculate Gradient from an OS Map
- Identify the start height and end height using contour lines or spot heights
- Calculate the vertical rise (difference in height)
- Measure the horizontal distance on the map and convert to real distance using the scale
- Divide: gradient = vertical rise ÷ horizontal distance
Exam Tip: Always show your working clearly. State the two heights, the difference, the measured distance and the conversion before dividing.
Cross Sections
A cross section (also called a transect or profile) is a side-on view of the landscape showing the shape of the land along a straight line.
How to Draw a Cross Section
- Identify the line — draw a straight line on the map between two points (A to B)
- Place paper — lay the straight edge of a piece of paper along the line
- Mark contour crossings — at every point where a contour line crosses the paper edge, make a small mark and write the height
- Also mark any rivers, roads, spot heights or other features crossed
- Transfer to graph paper — place the paper along the base (x-axis) of graph paper
- Set up the y-axis — choose an appropriate height scale (e.g. 1 cm = 50 m) covering the range of heights you recorded
- Plot the heights — for each mark on the paper, plot a dot at the correct height on the graph
- Join the dots — use a smooth, freehand curve (not a ruler) to connect the plotted points
- Label — add a title, label the x-axis (distance), y-axis (height in metres), and mark key features
Vertical Exaggeration
Because the horizontal distances are much larger than the vertical ones, cross sections usually use vertical exaggeration — the vertical scale is made larger than the horizontal scale. This makes it easier to see the landforms but means the slopes look steeper than they really are.
Calculating vertical exaggeration:
Vertical exaggeration = vertical scale ÷ horizontal scale
Example: Horizontal scale is 1:50,000. Vertical scale is 1 cm = 50 m (i.e. 1:5,000).
Vertical exaggeration = 50,000 / 5,000 = 10 times
Interpreting Cross Sections
Once drawn, you should be able to:
- Identify steep slopes (near-vertical sections) and gentle slopes (near-horizontal sections)
- Spot valleys (dips in the profile) and peaks (high points)
- Identify flat areas such as floodplains or plateaux
- Label and describe landforms visible in the profile
- Annotate human features such as settlement locations, road positions, and why they are found there
Common Features to Annotate
| Feature | How It Appears on a Cross Section |
|---|
| River valley | A dip (often V or U-shaped) in the profile |
| Floodplain | A flat section at the bottom of a valley |
| Ridge | A narrow high point |
| Plateau | A wide, flat high section |
| Escarpment | One steep side and one gentle side |
| Settlement | Usually on flat land near a water source |
| Road/railway | Follows valleys or passes through cols where possible |